The present invention relates to a method of forming a bottom electrode of a storage capacitor, and more particularly to a method of forming a bottom electrode of a storage capacitor in a semiconductor memory device such as a dynamic random access memory, wherein the storage capacitor has an increased capacity in unit area and shows a reduced leakage of current.
FIGS. 1A and 1B are fragmentary cross sectional elevation views illustrative of bottom electrodes of storage capacitors over base insulating films in sequential steps involved in a conventional method.
With reference to FIG. 1A, an etching stopper film 62 is formed over an upper surface of a base insulating film 61. A hole is formed in a base insulating film 61. A polysilicon contact plug 63 is filled into the hole of the base insulating film 61. A silicon electrode is formed over the etching stopper film 62 over the base insulating film 61, wherein a bottom of the silicon electrode is in contact with the top of the polysilicon contact plug 63. Further, hemi-spherical grains are formed on a surface of the silicon electrode to form a silicon stack electrode 64.
With reference to FIG. 1B, the silicon stack electrode 64 is exposed to a WF.sub.6 gas to substitute the hemi-spherical grains into tungsten W, whereby a tungsten stack electrode 94 is formed.
The above conventional method has the following disadvantages. Available metal is limited into tungsten which may shows a substitutional reaction with silicon (3Si+2WF.sub.6.fwdarw.2W+3SiF.sub.4). This reaction causes variation in volume, whereby the surface of the stack electrode 94 is deformed. Even illustration is not omitted, a dielectric film is formed on the deformed surface of the stack electrode 94. The deformed surface of the stack electrode 94 increases a leakage of current of the dielectric film.
In the above circumstances, it had been required to develop a novel method of forming a metal bottom electrode of a storage capacitor in a semiconductor memory device free from the above problem.